Impact hammers utilize a chisel-like tool for breaking hard materials. The tool is supported in a bushing or bushings for relative sliding movement. An end of the tool opposite the working end is impacted by a piston, directly or through an anvil, the piston being reciprocated within a cylinder and powered by air or hydraulic fluid. The stroke of the tool is relatively short, perhaps 1 to 2 inches. The hammer is typically attached to the end of a boom by which the hammer is moved and positioned against material to be chipped or broken.
The environment in which impact hammers are used is inimical to long wear of the hammer mechanism. Due to high forces and relatively high frequencies of impact, abrasive duct and debris from the material being broken or chipped are scattered with substantial force and velocity. The nature and construction of the hammer mechanism requires that the tool-supporting bushing or bushings be located near the work and therefore they are directly exposed to the abrasive dust and debris. These harsh materials are carried or work their way into the bushings by the reciprocating tool, and often work their way up into the cylinder itself and associated mechanisms. The abrasive nature of the dust and debris destroys the seals and bushings. This problem is particularly bad where the hammers are used in a horizontal or upward orientation, and when used in particularly harsh environments, such as in breaking up slag over molten metal, such as aluminum. Slag over molten aluminum tends to crumble and powder when impacted, and hot abrasive particles are projected upward and into the bushings, hammer mechanisms and seals. These and other corrosive substances with which the impact hammers may be used in industrial environments exacerbate the problems created by abrasive particles and dust, greatly shortening the life of the bushings, seals and other mechanisms, requiring frequent overhaul and replacement of parts.
Rubber dust caps for percussive hammers of the type used with masonry or the like are known (U.S. Pat. No. 2,944,523), as are flexible shields or boots for pile drivers or jackhammers to muffle the sound generated by their operation, and rubber-like safety attachments at the juncture of the tool and operating cylinder of hand-held pneumatic hammers, to protect the user in the event of a break in the tool shaft. See, for example, U.S. Pat. Nos. 2,685,874; 3,975,918; and Swedish Patent No. 77,382, dated May 23, 1933. These structures were not intended to and would not provide adequate protection to the seals and other working parts of the mechanism of a boom-supported impact hammer that is used in very hot and very harsh environments and that applies very high impact forces that cause shattered particles of hot and hard abrasive material to impinge against the hammer mechanism.